Comparison of two spectra based on their 6708 Å lithium lines: One with the lithium line and another without. Panel a shows an M6 spectrum with a lithium absorption line. An M6 spectrum without lithium is shown in panel b for comparison. The small windows in each panel zoom in on the region that containing the 6708 Å lithium line. The atmosphere parameters from the LAMOST 1D pipeline are labeled.